The present invention generally relates to a fluid flow control device and, in particular, relates to such a device for producing a fluid flow having uniform pressure drop across the cross-section thereof.
The control of fluid flow, while of importance in many fields, is of primary importance in the field of liquid chromatography. In a liquid chromatography system a fluid, usually comprising a carrier fluid and a sample fluid, is injected into a separation column, such columns are generally known in the art. As well known, as the fluid passes through the column the constituents of the sample fluid travel therealong at different velocities due to their various rates of interaction with the packing material of the column. The intended result of this procedure is to provide an output flow of the various individual constituents one after the other. That is, the output of the column would initially contain only the least retained constituent and thereafter the next to the least retained constituent would flow out and etc. Ideally, there would be a sharp cut off at the interface between constituents. However, such is not always the case, for in conventional chromatography systems the transition from one constituent of the sample fluid to the next is often gradual and indistinct.
The transition problem between constituents can result from the fact that, in conventional columns, the fluid flow along the column is usually constrained to a core segment of the packing material. The effect of such a constraint is an inefficient separation of constituents. The inefficiency arises because the core segment quickly becomes saturated and constituents which should be slowed after traveling a certain length along the columns continue to flow since they cannot interact with the saturated packing material of the core segment. Thus the output of the constituents are, at the transitions therebetween, blended and indistinct. The capacity of the column for increased loads of the sample constituents is also impaired because only the core segment of the packing material is being utilized.
The constrained fluid flow through a liquid chromatography column also reduces the useful life of that column. The useful life of a given packing material is finite since, when a fluid is passed thereover, a small amount of the constituents of that fluid may be irreversibly retained. Thus the total amount of fluid passed over a portion of packing material throughout its useful life is also finite. Hence, it is easily understood that if, for a given cross-section of packing material, all the fluid passed thereacross is confined to a core segment thereof the useful life of that cross-section of material is less than if the same amount of fluid were distributed across the entire cross-section thereof.